DRO and Edgefinder questions

tailshaft56 · Post by **tailshaft56** » Sun Jan 17, 2010 11:59 pm

I'm building the Z mount for the quill. What does everyone think is best. Mount the scale solid and move the reader or mount the reader solid and move the scale? I would prefer to make the scale solid but I'm a little worried about constantly flexing of the cable.

As to the edge finder what's the best way to be dead nuts on?

TIA

pete · Post by **pete** » Mon Jan 18, 2010 1:35 am

Tailshaft,
My vote, Mount the scale solid, Thats how Mitutoyo engineered their add on quill scale for mills.

Pete

Post by **GlennW** » Mon Jan 18, 2010 5:38 am

Use a DTI to find an edge if you need to be dead nuts.

There are various methods.

One fairly simple method would be to lightly clamp a smaller size ring gauge to the table. Sweep the bore of the ring gauge and center the spindle over it and zero the DTI. Now move toward the edge of the part, and sweep the spindle back and forth and feed in until the needle reads zero again. Now you are exactly one half the diameter of the ring gauge from the true edge.

The same can be done using a .200" (or whatever) gauge block with sandwiched between two other blocks. Or a .200" gage block sandwiched against the edge of the part and another gauge block.

Lots of different and accurate methods using a DTI.

A quality "kick out" type edge finder would be the next best if properly used.

"Dead nuts" accuracy is also dependant on the surface finish of the edge being located.

tailshaft56 · Post by **tailshaft56** » Mon Jan 18, 2010 1:23 pm

Actually I was refering to the use of the edge finder. I sure I can get within a thou or so but I'm not sure of the absolute edge. Do you consider the point at which the EF runs concentric as the edge or the little movement later when it begins to kick over?

mechanicalmagic · Post by **mechanicalmagic** » Mon Jan 18, 2010 1:39 pm

tailshaft56 wrote:Do you consider the point at which the EF runs concentric as the edge or the little movement later when it begins to kick over?

I have always believed that it must kick over to be on the edge. My logic is this; if there is a gap it's not there yet, if it's .00001" beyond, it's kicked.

Dave J.

Post by **Harold_V** » Mon Jan 18, 2010 1:57 pm

tailshaft56 wrote:Actually I was refering to the use of the edge finder. I sure I can get within a thou or so but I'm not sure of the absolute edge. Do you consider the point at which the EF runs concentric as the edge or the little movement later when it begins to kick over?

There isn't a doubt in my mind, having used edge finders for more than 50 years, that they are speed sensitive. I have found that my ½" diameter edge finder responds best @ 2,000 rpm, so that's where I use it.

I suggest you experiment with yours, trying various speeds, to see how it behaves.

A little tip, that makes sense, but may evade some people. When you set your edge finder, set the dial reflecting the radius, so when you crank to "0", you're on the edge of the part. I run a BP, so I set my dial @ 150, so 1¼ turns puts me on location. By doing so, you eliminate the outside chance that you will lose registration (adding miniscule error) when resetting the dial.

I am comfortable that I can pick up an edge within .0005" consistently. The error on locking the slides on a BP will generally be greater than the ability to locate an edge properly. Don't lose too much sleep over missing by a few tenths unless you are working to tenths.

Harold

thedieter · Post by **thedieter** » Mon Jan 18, 2010 4:45 pm

I am interested in this subject as I am in the market for a set of edge finders/wigglers. I have been wondering about how one knows if when the edge finder kicks out, it is not already too far.

Best regards, Jack

Post by **GlennW** » Mon Jan 18, 2010 5:52 pm

That's why I used the DTI. I found the edge of a 1-2-3 block with it and then zero'd the dial. I then switched to a Starret .2" dia edge finder and found the edge with that and compared dial readings. Mine is most accurate at 1000 rpm.

It seemed to me that you need a reference to develop a technique.

Sort of like practicing with a micrometer on an unknown length piece of stock. You won't really know if you are using it correctly unless you use a standard or something of known dimension to practie with to develop a feel for it.

Just my .02

calgator · Post by **calgator** » Mon Jan 18, 2010 6:04 pm

jack,

check out the youtube video on how to use an edge finder.

http://www.youtube.com/watch?v=f0od-cp_9dg

mechanicalmagic · Post by **mechanicalmagic** » Mon Jan 18, 2010 7:59 pm

thedieter wrote:I have been wondering about how one knows if when the edge finder kicks out, it is not already too far.

Practice and experience.

I've been using edge finders for so long I just trust my method. But is it right? SO, time for a test.

I got a Chinese edge finder, verified it was .2000" +-a tenth.
Cleaned off a .100" gage block, it's .1001".
Off to the mill, held the gage block in a toolmaker's vise.
Using my preferred method (just after kick over), I was getting perfect repeatability with a resolution of .0005" on the DRO, in both directions. However I was measuring .301". OOPS, what's up? Noticed the edge finder was hitting at the tip only on one side. Back with a DTI, and I trued the gage block to the spindle.
Now I get .2995" repeating. Good enough for me. I'll just add .0002" in my head, the DRO won't read that resolution.

I did try and use the return to concentric way, but repeatability was all over the map. Perhaps because I didn't want it to work that way.

For those new to the game I would you suggest you try on a gage block or ground parallel of known thickness. Practice will provide skill. And don't watch the DRO or dial.

Dave J.

thedieter · Post by **thedieter** » Mon Jan 18, 2010 11:02 pm

Thanks for the useful tips. The video is informative. I have worked with some very skilled machinists and watched them use edge finders but not used one myself. I think the "old school" edge finder will do fine for me as I don't want anything to do with batteries.

Besr regards, Jack

Post by **Harold_V** » Tue Jan 19, 2010 1:05 am

thedieter wrote:Thanks for the useful tips. The video is informative. I have worked with some very skilled machinists and watched them use edge finders but not used one myself. I think the "old school" edge finder will do fine for me as I don't want anything to do with batteries.

Besr regards, Jack

I commented that I've been using edge finders for more than 50 years.

I can honestly say that I have never had to replace a battery in any of my edge finders (one a ½" diameter unit, the other a Starrett with a .100" disc, and a .250" ball. There is also a third attachment, a pointed end (wiggler) , which gets more use than either the disc or ball.
These devices work perfectly well----generally with more precision than the machine on which it is used. I recommend them highly, and wouldn't even consider owning one with a battery.

Harold